Lemma 2.9 [1]} If \(N(r,0;f^{(k)}\mid f\ne 0)\)  denotes the counting function of those zeros of \(f^{(k)}\)  which are not the zeros of \(f\) , where a zero of \(f^{(k)}\)  is counted according to its multiplicity then
\(N(r,0;f^{(k)}\mid f\ne 0)\le k\overline{N}(r,\infty ;f)+N(r,0;f\mid <k)+k\overline{N}(r,0;f\mid \ge k)+S(r,f).\) 

